Digital transmission techniques often use either quadrature phase shift keying (QPSK) or quadrature amplitude modulation (QAM) to modulate data. The modulated data sometimes has undergone additional encryption methods prior to modulation to make its recovery accurate and robust. The Digital Video Broadcasting (DVB) standards use QPSK and QAM techniques for data transmission.
The Digital Video Broadcasting standards consortium is a group that defines the standards for various transmission systems. One of those standards is used for digital cable transmission, the DVB-C standard. A second generation digital cable standard, the DVB-C2 standard, uses Reed-Muller encoding of information followed by mixing with a pseudo-noise (PN) sequence. A receiver needs to remove the effect of the PN sequence prior to recovery of the information bits.
A frame header of Forward Error Correction (FEC) is used in the DVB-C2 transmission Standard to support Adaptive Coding and Modulation (ACM) or Variable Coding and Modulation (VCM) in each FEC block. The FEC frame header (FECFrame) is attached in front of each FECFrame or two consecutive FECFrames to indicate the coding rate, modulation type and physical layer pipe identifier to a receiver. Thus, FECFrame detection is required in a DVB-C2 receiver. Two types of FEC frame headers can be generated in an encoder. First, in robust mode, the FEC frame header is generated using quadrature phase shift keying (QPSK). Second, in high efficiency mode, the FEC frame header is generated using 16 quadrature amplitude modulation (16-QAM). Based on the type of the FECFrame header, FECFrame detection methods and apparatus are described in this invention, suitable for use with the DVB-C2 standard.